1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for controlling gas flow to a processing chamber.
2. Description of the Related Art
Accurate control of gas flows is an important process control attribute critical to many microelectronic device fabrication processes. Providing gas between a substrate and a substrate support in a semiconductor processing chamber is a well-known method for improving heat transfer between the substrate and the substrate support, thereby enhancing the precision of substrate temperature control and uniformity. Additionally, precise control of process gas flows into the processing chamber are required in order to obtain desired processing results, particularly as critical dimensions and film thicknesses shrink. Furthermore, gases may be added to processing chamber effluent streams to mitigate the environmental impact of substrate processing. Good control of the gases added to the effluent stream is necessary to ensure both cost effective and proper remediation.
Conventional gas delivery systems used with semiconductor processing chambers generally include a mass gas flow meter (MFC) as the primary flow regulation device. However, the accuracy of MFC's may be affected by a plurality of factors that contribute to an uncertainty of the actual gas flow. For example, the accuracy of the MFC will typically vary with changes in temperature, line pressure and volume. Deviation from the gas flow set point due to MFC inaccuracy may contribute to processing defects, poor emission control and inefficient waste of costly gases.
Although conventional pressure control systems have proven relatively reliable, field experience with the existing technology has increased the demand for more accurate measurement of flow. For example, poor control of gas flows used in backside substrate cooling applications may result in poor substrate temperate control, thereby causing poor film deposition or etching results, which cannot be tolerated in next generation circuit designs.
Moreover, conventional gas delivery systems generally have fixed conduits for routing gases from the gas sources into the processing chamber. Thus, only a predefined combination of process gases may be delivered to the processing chamber at any time. Such fixed gas delivery routing prevents process flexibility. For example, processing chambers having fixed gas delivery routes may not be able to accommodate new or revised process recipes that require a different combination of process gases. Additionally, a processing chamber having a fixed gas delivery route designed to deliver one combination of process gases to perform a first process may not be able to perform a second process that utilizes a different combination of gases, thereby preventing the processing chamber from being utilized for other processes and causing the FAB owner to invest in addition capitol equipment. Thus, it would be desirable to devise a gas delivery system having greater flexibility.
Therefore, there is a need for an improved method and apparatus for controlling the delivery of gases to a semiconductor processing system.